Process for sulfur removal from refinery off gas

ABSTRACT

Organic sulfur compounds contained in refinery off gas streams having either high or low concentrations of olefins are converted to hydrogen sulfides which can be then be removed using conventional amine treating systems. The process uses a catalytic reactor with or without a hydrotreater depending on the olefin concentration of the off gas stream. The catalytic reactor operates in a hydrogenation mode or an oxidation mode to convert a majority of organic sulfur compounds into hydrogen sulfides.

RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.61/246,592, filed on Sep. 29, 2009, the entire contents of which areincorporated herein by reference in its entirety.

TECHNICAL FIELD

The present invention relates to the removal of sulfur compounds fromgases derived from petroleum refinery processes. In one respect, itrelates to processes for removing sulfur compounds from refinery off gasstreams to create more valuable hydrocarbon containing feed gases, whilein another respect it relates to processes to convert organic sulfurcompounds to hydrogen sulfides which can be then be removed usingconventional amine treating systems.

BACKGROUND

The petroleum refining industry generates large quantities of low valueprocess gases which typically have high concentrations of sulfurcompounds. These refinery off gas (ROG) streams, as they are known, aregenerated from various “secondary” processing technologies used in oilrefining such as catalytic cracking, hydro-treating and delayed cokingprocesses. The largest quantity of ROG streams are derived frompetroleum cracking units.

ROG streams are comprised of a wide range of gases including hydrogen,carbon monoxide, carbon dioxide and hydrocarbons with more than onecarbon atoms including both saturated (paraffins) and unsaturated(olefins) hydrocarbons, such as ethane and ethylene respectively. Thecontent of ethane and ethylene can be as high as 30% and the content ofhydrogen is typically in the range of 15 to 50%. The sulfur compoundsare typically hydrogen sulfide (H₂S), carbonyl sulfide (COS) and organicsulfur compounds such as mercaptans, thiophenes and sulfides. Theconcentration of H₂S can be greater than 1% by volume and theconcentration of organic sulfur compounds can be several hundred partsper million.

Due to the lack of effective technologies for converting ROG streamsinto more valuable products or useful feed streams, many of these gasstreams are used for their fuel value or, in many cases, simply flared.However, even the simple combustion of ROG streams containing highconcentrations of sulfur compounds can result in the emission of toxicor other environmentally undesirable gases such as sulfur oxidecompounds. Stringent environmental regulations for the emission of theseundesirable compounds require that refineries invest in expensivescrubbing systems for more complete sulfur removal from ROG streamsprior to or after combustion.

The conversion of high sulfur ROG streams into more valuable low sulfur,hydrocarbon/hydrogen containing streams can reduce energy losses,provide valuable feed streams for further processing, and eliminate manyof the environmental concerns associated with the combustion of highsulfur ROG streams. Moreover, since many hydrocarbon conversionprocesses are catalytic using expensive metal catalysts, the sulfurconcentration must be lowered to avoid poisoning the metal catalysts inorder to effectively use the hydrocarbon/hydrogen content in the ROGstreams as feed gases.

Generally, ROG streams are taken from multiple refinery processingunits, collected and desulfurized at a central location in the refinery.However, ROG streams may be required to be taken from a single refineryprocess and treated and/or used without mixing with other off gasstreams due to its specific gas composition.

Many refineries already use amine sulfur removal technology. Aminesulfur removal technology is well known and refers to a group ofprocesses that use aqueous solutions of various amine compounds(commonly referred to simply as amines) to remove H₂S and carbon dioxide(CO₂) from sulfur containing gases. While these amine systems are veryeffective at removing H₂S, they are less effective in removing organicsulfur species such as mercaptans, thiophenes, sulfides, and othercomplex sulfur compounds. For the removal of these organic sulfurcompounds, the use of caustic removal systems is generally needed.Caustic removal systems are expensive, use caustic reagents such aspotassium hydroxides, which are considered toxic, become consumed andrequire safe environmental disposal.

Another desulfurization option for fuel gas streams containing organicsulfur compounds is a two-step process consisting ofhydrodesulfurization, e.g. the conversion of organic sulfur compounds toH₂S, and the subsequent removal of the H₂S with an amine based system ora solid sulfur adsorbent such as ZnO. This approach is typically usedfor the desulfurization of natural gas feedstocks and ROG streams havinglow sulfur levels (e.g. 5-10 ppm) such as when natural gas is used as afeedstock in a steam methane reformer for the production of hydrogen.Conventional hydrotreaters in steam methane reformer based hydrogenplants operate at about 300° C.-400° C. utilizing waste heat from thesteam methane reforming plant to preheat the feed to the hydrotreater.The catalyst used in conventional hydrotreaters is typically a CoMo orNiMo catalyst.

As mentioned above, the organic sulfur compounds in the ROG streams canbe first hydrogenated in a hydrotreating process to form H₂S and thensubsequently removed with conventional amine sulfur removal systems.However, for efficient hydrotreating of organic sulfur compounds, heatmust be supplied and removed both economically and reliably for thesystem to convert organic sulfur to H₂S. Since the ROG streams aretypically received at low pressures, such as 5-10 bar, the hydrotreatermust be operated at elevated temperatures in the range of 290°-370° C.to ensure complete conversion of the organic sulfur species. Controllingthe temperature within the hydrotreater becomes a key to finding a costeffective sulfur removal process because waste heat is not alwaysavailable.

Achieving the high temperature needed for hydrogenation of organicsulfur compounds without using an external heat source can be a problem.Hydrogenation of gas streams containing olefins is an exothermicreaction thereby providing heat to the reaction. If the ROG stream doesnot contain sufficient concentration of olefins, the hydrogenationsystem will not be able to maintain the proper temperature forconversion of the organic sulfur compounds to H₂S and external heat mustbe provided to the reactor. If the ROG stream contains too high of aconcentration of olefins, the hydrotreating unit can overheat causingthe catalyst to be damaged or destroyed.

One solution to this problem is to dilute the high olefin containing ROGstream with a recycle stream from the hydrotreater product. This howeverrequires a recycle compressor which complicates the system, makes itless reliable and increases the cost. Also, ROG streams usually havesignificant composition variability which makes a hydrotreater withrecycle compressor based system difficult to design and control. Last,due to the typical low pressure of ROG feed streams, the hydrotreateroperates at low space velocities, such as less than 1000 hr⁻¹, whichrequire that the reactors be extremely large adding additional capitalcosts. Space velocity is defined here as the volumetric flow of ROGstreams at standard conditions (standard m3/hr) divided by the reactorvolume (m³). Since the cost of the catalytic reactor catalyst issignificantly higher than the cost of the conventional hydrotreatercatalyst, the better solution could be a combination of the two reactorsdepending on the management of operating factors such as catalyst cost,pressure and olefin concentration.

Thus the present invention provides a sulfur processing system that isflexible enough to process ROG streams having varying sulfurconcentrations, varying organic sulfur compounds, and varying olefincontent while still being economical. This invention uses nocontinuously supplied external heat source for the hydrogenationreaction, eliminates the need to use recycle streams to the hydrotreaterto control temperature, and allows for the use of smaller reactorsreducing capital costs. Last, the present invention allows for theelimination of a caustic sulfur removal systems and replaces them with aprocess employing a catalytic reactor used with an amine absorber thatis more reliable, easier to operate and can be integrated with theexisting refinery amine system.

SUMMARY OF THE INVENTION

The present invention provides a process for removing sulfur compoundsfrom refinery off gas streams to create more valuable hydrocarboncontaining feed gases. This invention provides flexibility of operationto address; (a) when the ROG stream contains such low concentrations ofolefins that the reaction in the hydrotreater cannot be maintained attemperatures sufficient to convert organic sulfur compounds to H₂Swithout externally supplied heat, and (b) when the ROG stream containssuch high concentrations of olefins that the temperature in theconventional hydrotreater becomes too high and damages the catalyst or(c) when the olefin composition variability is such that at any giventime the ROG stream will fall into either the (a) or (b) category aboveor (d) when the ROG steam contains olefin concentrations that can beprocessed in a conventional hydrotreater but the cost of thereactor/catalyst needed for the catalytic reactor is lower than theconventional hydrotreater reactor.

According to one embodiment of this invention, a process for the removalof sulfur compounds comprising hydrogen sulfide (H₂S) and organic sulfurcompounds from a refinery off gas feed stream containing hydrogen and alow concentration of olefins is provided, the process comprising:

a) removing at least a portion of the H₂S from the feed stream bypassing the feed stream through an amine absorber to produce a H₂Sdepleted stream;

b) feeding a first portion of the H₂S depleted stream into a catalyticreactor with the addition of oxygen to produce a hot effluent streamexiting the catalytic reactor at a temperature of between about 340° C.and 450° C.;

c) feeding a second portion of the H₂S depleted stream into the hoteffluent stream exiting the catalytic reactor to form a preheatedcombined stream, wherein the first portion and second portion are mixedin quantities such that the combined stream is fed into a hydrotreaterto maintain the temperature of the hydrotreater to between about 340° C.and 450° C. at the pressure employed;

d) converting a majority of the organic sulfur compounds to hydrogensulfide in the hydrotreater;

e) cooling the product gas stream exiting the hydrotreater; and

f) feeding the cooled product gas stream to an amine sulfur removalsystem to remove the H₂S and produce a hydrocarbon product stream.

In another embodiment of this invention, a process is provided for theremoval of organic sulfur compounds from multiple refinery off gasstreams containing at least olefins and sulfur compounds including H₂Sand organic sulfur compounds, wherein a first off gas feed streamcontains a high concentration of olefins and a second off gas feedstream contains a low concentration of olefins, the process comprising:

a) feeding the first feed stream to an amine absorber to remove at leastpart of the H₂S to produce a first H₂S depleted stream; b) feeding thesecond feed stream to an amine absorber to remove at least part of theH₂S to produce a second H₂S depleted stream

c) splitting the first H₂S depleted stream into a first split stream anda second split stream;

d) feeding the first split stream into a catalytic reactor at atemperature of between 340° C. and 450° C. to convert a majority of theorganic sulfur compounds to H₂S at the pressure employed and removing ahot first organic sulfur depleted stream from the catalytic reactor;

e) combining the second split stream and second H₂S depleted stream aremixed in quantities such that the resulting combined stream is fed intoa hydrotreater and maintains the temperature of the hydrotreater tobetween about 340° C. and 450° C. at the pressure employed andconverting the organic sulfur compounds into H₂S;

f) removing a second organic sulfur depleted stream from thehydrotreater;

g) combining the first organic sulfur depleted stream and the secondorganic sulfur depleted stream to form a combined organic sulfurdepleted stream;

h) cooling the combined organic sulfur depleted stream; and

i) feeding the cooled combined organic sulfur depleted stream to anamine sulfur removal system to remove the H₂S and produce a product gasstream.

In yet another embodiment, a process is provided for the removal of H₂Sand organic sulfur compounds from a refinery off gas feed streamcontaining at least hydrogen, and a high concentration of olefinscomprising:

a) removing at least a portion of the H₂S from the feed stream bypassing the feed stream through an amine absorber to produce a H₂Sdepleted stream;

b) feeding the H₂S depleted stream into a catalytic reactor at atemperature between 340° C. and 450° C. to convert a majority of theorganic sulfur compounds to H₂S at the pressure employed;

c) cooling the product gas stream exiting the catalytic reactor; and

d) feeding the cooled product gas stream to an amine sulfur removalsystem to remove the H₂S and produce a product gas stream.

In yet another embodiment, a process is provided for the removal of H₂Sand organic sulfur compounds from a refinery off gas feed streamcontaining hydrogen, carbon oxides and olefins comprising:

a) removing at least a portion of the H₂S from the feed stream bypassing the feed stream through an amine absorber to produce a H₂Sdepleted stream;

b) determining the olefin concentration of the feed stream or H₂Sdepleted stream;

c) determining the process flow based on the concentration of olefins inthe feed stream or the H₂S depleted stream such that;

(I) when the olefin concentration is determined to be 3% or less,

-   -   (i) feeding a first portion of the H₂S depleted stream with the        addition of oxygen into a catalytic reactor to maintain the        temperature of the catalytic reaction between 340° C. and        450° C. at the pressures employed and convert a majority of the        organic sulfur compounds to H₂S;    -   (ii) feeding a second portion of the H₂S depleted stream into a        hot effluent stream exiting the catalytic reactor;    -   (iii) feeding the hot effluent stream into a hydrotreater and        maintaining a temperature of between 340° C. and 450° C. to        convert a majority of the organic sulfur compounds to H₂S and        produce an H₂S rich product gas stream;    -   (iv) cooling the H₂S rich product gas stream exiting the        hydrotreater; and    -   (v) feeding the cooled H₂S rich product gas stream to an amine        sulfur removal system to remove the H₂S and produce a sulfur        depleted product stream; or

(II) when the olefin concentration is determined to be 5% or greater,

-   -   (i) feeding the H₂S depleted stream into a catalytic reactor and        maintaining the temperature to between about 340° C. and 450° C.        to convert a majority of the organic sulfur compounds to H₂S at        the pressures employed and produce a product gas stream; (ii)        directing the product gas stream to bypass the        hydrotreater, (iii) cooling the product gas stream; and    -   (iv) feeding the cooled product gas stream to an amine sulfur        removal system to remove the H₂S to produce a sulfur depleted        product stream.

In a final embodiment, a process is provided for the removal of H₂S andorganic sulfur compounds from a refinery off gas feed stream containingat least hydrogen, and a low concentration of olefins wherein thehydrogen to olefin molar ratio is greater than 0.5, comprising:

a) removing at least a portion of the H₂S from the feed stream bypassing the feed stream through an amine absorber to produce a H₂Sdepleted stream;

b) feeding the H₂S depleted stream into a catalytic reactor at atemperature between 340° C. and 450° C. to convert a majority of theorganic sulfur compounds to H₂S at the pressure employed;

c) cooling the product gas stream exiting the catalytic reactor; and

d) feeding the cooled product gas stream to an amine sulfur removalsystem to remove the H₂S and produce a product gas stream.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and theadvantages thereof, reference should be made to the following DetailedDescription taken in conjunction with the accompanying drawings inwhich:

FIG. 1 is a schematic illustrating an embodiment of the invention.

FIG. 2 is a schematic illustrating another embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The process and system of the present invention is directed to theflexible and effective use of olefin containing ROG streams. ROG streamscome from multiple sources such as from fluidized catalytic cracking(FCC) units, hydrocracking units, and delayed coking units and containvarying types and concentrations of sulfur compounds. These sulfurcompounds, including various organic sulfur compounds as describedbelow, must be removed prior to either further processing of the ROGstream or the use of the ROG stream as a fuel gas.

ROG streams coming from various refinery processes can be combined intoa single ROG stream or can be segregated between those containing higholefin concentrations and those containing low olefin concentrations. Inmost refineries, the ROG streams will naturally have high or low olefinconcentrations based on their source. The olefin concentration willdetermine the optimal sulfur removal process and either a single streamor two streams with varying olefin concentrations can be simultaneouslyprocessed. As used herein, ROG streams “having low concentrations ofolefins” have olefins concentrations of 3% or less by volume and those“having a high concentrations of olefins” have olefins concentrations of5% or more by volume. Small variations on these concentrations arepossible based on the final composition of the off gas streams as isunderstood. ROG streams having a middle range of olefins, such as about4% by volume, can normally be treated with conventional hydrotreatingtechniques but due to low pressures the space velocity of theconventional hydrotreater can be less than 1000 hr⁻¹. In accordance withthe present process, sulfur compounds can be effectively removed fromall typical ROG streams without significant capital investment orprocess modification by integration into the existing refinery sulfurremoval system and subsequent Claus sulfur removal system. Afterremoval, the sulfur depleted stream can be used as a fuel gas or used asa feed gas stream in further processing. When used as a fuel gas, therefineries can achieve acceptable sulfur oxides emissions.

The present process is integrated into conventional sulfur removingsystems used in refineries of the type using sulfur absorbers. Suchsystems are typically amine sulfur removal systems that use aqueoussolutions of amines with the most commonly used amines beingalkanolamines, monoethanolamine, diethanolamine, andmethyldiethanolamine. A typical amine gas treating process includes oneor more absorbers, regenerator(s) and accessory process equipment. Inthe absorber, the down flowing amine solution absorbs H₂S and CO₂ fromthe up flowing sulfur containing gas (sour gas) to produce a sweetenedgas stream (i.e., an H₂S depleted stream) as a product gas and an aminesolution “rich” in the absorbed acid gases. The resultant rich aminesolution is then routed into the regenerator (generally a stripper witha reboiler) to produce regenerated or “lean” amine solution that isrecycled for reuse in the absorber. The stripped overhead gas productfrom the regenerator is a concentrated H₂S and CO₂ stream. This H₂S-richstripped gas stream is typically routed into a conventional Claus sulfurremoval process to convert the H₂S it into elemental sulfur. In someplants, more than one amine absorber unit may share a common regeneratorunit. The amine treating system is shown in FIG. 1 within the doted boxand is not individually considered part of this invention.

As used herein, the term “organic sulfur compounds” is intended toinclude simple, complex and cyclic organic sulfur molecules and specieswherein a central sulfur atom is directly attached to one or more carbonatoms. Examples of such compounds include but are not limited to,organosulfur acids, (such as sulfonic, sulfinic and sulfenic acids) andnon-acid organic sulfur compounds (such as sulfides, sulfoxides, andsulfones). Many of the sulfur compounds typically found in refineryprocess gases are know by more common nomenclature such as sulfides,sulfites, thiosulfites, thiophines, mercaptans, disulfides and dialkylsulfides. It is these organic sulfur compounds that make conventionalsulfur removal processes less effective.

According to this invention, ROG streams are treated by the appropriatecombination and use of a catalytic reactor and a conventionalhydrotreating reactor to convert the organic sulfur compounds within thestreams into H₂S. The catalytic reactor used in this invention isdisclosed in U.S. Pat. Nos. 7,547,422 and 7,037,485 and offers dual modeoperation (hydrogenation and oxidation) using the same catalyst andefficient heat integration. The teachings of U.S. Pat. Nos. 7,547,422and 7,037,485 are incorporated herein by reference. The catalyticreactor that operates at space velocities of greater than 10,000 hr⁻¹,preferably greater than 50,000 hr¹, and can be used with or without aconventional hydrotreating unit to convert the organic sulfur compoundsto H₂S. The catalytic reactor used herein can operate in a dual modeeither in hydrogenation mode without oxygen or in oxidation mode withoxygen.

The catalytic reactor employs known catalysts that contain one or moregroup VIII metal, preferably platinum, rhodium, palladium, nickel orruthenium. The structure of the catalyst is preferably a monolith madeof reticulated foam, honeycomb or a corrugated foil wound in spiralconfiguration although other structures can be employed. Catalyst coatedbeads, pellets, or ceramic monoliths in the form of reticulated foam orhoneycomb structure can also be used.

Generally, the ROG feed stream containing hydrogen is first heated tobetween about 150-250° C. and then fed into a communicating system of acatalytic reactor and a conventional hydrotreating reactor. When the ROGfeed stream has a low concentration of olefins, the heat generated bythe conversion reaction of olefins to paraffins in a conventionalhydrotreater is not sufficient to maintain reactor temperature at therequired range of about 340-400° C. In order to generate the requiredheat, part of the ROG feed stream can be directed into the catalyticreactor where oxygen, and optionally steam, is added. The heat neededfor the reaction is generated in the catalytic reactor by the hydrogencombustion with oxygen. The hot reactant gas exiting the catalyticreactor can then be added to the remaining ROG feed stream and fed tothe hydrotreater at the higher temperature so the temperature rise inthe hydrotreater (due to conversion of olefins) raises the temperatureat the exit of the hydrotreater to the desired range of about 340°-400°C. The ROG feed stream will typically contain hydrogen well in excess ofthe amount required for the olefin hydrogenation, sulfur conversion andoxygen combustion reactions, but if insufficient hydrogen is present forcompletion of these reactions, hydrogen can be added as required. Insuch situations, hydrogen can be added from another hydrogen containingstream, from the existing on site hydrogen production if available, orfrom storage. The organic sulfur compounds are converted into H₂S atthese hydrotreater temperatures. The effluent stream (or product gas)from the hydrotreater is cooled to near-ambient temperature and fed to aconventional amine sulfur recovery unit for H₂S removal.

If the ROG feed stream contains a high concentration of olefins, it canbe fed directly to the catalytic reactor which can operate in eitherhydrogenation mode (no oxygen) or dual mode (with oxygen) as needed. Ifthe hydrotreater is operated at overly high temperatures such as may begenerated by the conversion of high concentrations of olefins, the heatsensitive hydrotreating catalyst will be damaged or destroyed. Thus, inthis case, the hydrotreater is bypassed. The operation mode of thecatalytic reactor, hydrogenation or oxidation, will depend on thepressure of the ROG feed stream and the organic sulfur concentration.The hydrogenation of olefins is favored at higher pressures and lowersulfur concentrations. If the stream condition is such that the extentof olefin hydrogenation does not generate sufficient heat to achieve atleast about 340° C. at the reactor exit, oxygen may be added to combustwith hydrogen and supply additional heat to meet the temperaturerequirements. The oxygen addition is controlled so that the reactor exittemperature is maintained at about 340°-400° C. Hydrogen is present inexcess to ensure that the oxygen conversion is substantially complete.Hydrogen is preferably present in the ROG feed stream in a hydrogen toolefin molar ratio of greater than 0.5 and, more preferably, greaterthan 1. Generally, if the pressure of ROG feed stream is greater than 10bar, and more preferably greater than 15 bar, the catalytic reactor willoperate in hydrogenation mode. If the pressure of ROG feed stream isless than 10 bar, the catalytic reactor will operate with some oxygenaddition. The oxygen addition is used to provide supplemental heat byreaction of oxygen with hydrogen. The amount of oxygen added will dependon the extent of the hydrogenation reaction desired and will becontrolled such that the reactor exit temperature is maintained betweenabout 340° C.-450° C. The majority of organic sulfur compounds in theROG feed stream are converted into H₂S in either mode of operationthereby efficiently using the heat energy of the feed and reducing therisk of catalyst damage. The effluent stream leaving the catalyticreactor is again cooled to near ambient temperature and is fed to aconventional amine sulfur recovery unit for H₂S removal as describedabove.

The process of this invention is best understood by reference to theFigures. FIGS. 1-2 illustrate the basic process flow of two embodimentsof the present invention. While all essential aspects of the process areshown, additional nonessential aspects or features may be present as isunderstood and readily apparent to one skilled in the art. The detailsof the conventional amine treating system are not described since theyare well known to one skilled in the art.

Now referring to FIG. 1, a sulfur removal process of one embodiment ofthis invention is described for situations where there is a singleolefin containing ROG feed stream. In this embodiment, the ROG streamcan either come directly from one of the refining processes or can becollected from multiple processes and fed as a collected stream. Whenorganic sulfur compounds such as mercaptans, thiophenes and disulfides,are present in combination with H₂S, the ROG feed stream (3) is fed toabsorber (12) of the amine sulfur removal system (hereinafter “aminetreater”) which reduces the H₂S concentration to less than about 50 ppm,preferably less than 30 ppm, in the exiting H₂S depleted stream (5). Theabsorber (12) may already be associated with or integrated into theamine treater, but will typically be a separate unit added for proposesof conducting the inventive process. Since most organic sulfur compoundscannot be substantially removed in the amine treater and may remain inamounts of greater than 50 ppm (and in amounts as high as severalhundred ppm), additional processing is required.

The H₂S depleted stream (5) leaving absorber (12) and continuing tohaving high concentrations of organic sulfur compounds is firstpreheated in recuperator (11) or other suitable heat exchanger, and thensplit into two streams shown as streams (15 and 6). First split stream(15) is sent to the catalytic reactor (2) and second split stream (6) issent to the hydrotreater (4). A sufficient amount of oxygen isintroduced into first split stream (15) through line (16) before passinginto the catalytic reactor (2) to operate the reactor in the oxidationmode and to provide the needed heat for the conversion reaction.Optionally, first split stream (15) may be preheated in a conventionalstart-up heater (14) to be heated during start up. The flow of oxygenthrough line (16) and first split stream (15) are adjusted to providesufficient reaction with the hydrogen present in ROG feed stream (3) toproduce water and heat to raise the temperature within catalytic reactor(2) and of the effluent stream (7) leaving catalytic reactor (2) tobetween about 340° C.-450° C. By maintaining the reaction temperature ofthe effluent stream (7) above about 340° C., the majority of the organicsulfur compounds, typically more than 60%, and preferably greater than70%, are converted to H₂S.

The effluent stream (7) exiting the catalytic reactor (2) is then mixedwith the second split stream (6) and is fed through line (67) tohydrotreater (4). The mixing of the hot effluent stream (7) exiting thecatalytic reactor (2) and the cooler second split stream (6) results ina preheated combined stream (67) with sufficiently high temperature sothat the hydrotreater (4) can convert the organic sulfur compounds toH₂S, even with the low concentration of olefin present. The temperatureof the combined stream (67) is controlled to be between 200° C. and 350°C., more preferably between 225° C. and 275° C. by the volume of gasfrom second split stream (6) added to effluent stream (7). Depending onthe olefin concentration of ROG feed stream (3), the volume of gas fromfirst split stream (15), the volume of gas from second split stream (6),and the volume of oxygen added to first split stream (15) can beadjusted to maintain the desired temperature range at the hydrotreater(4) entrance. This can be determined by one skilled in the art bymonitoring the temperatures of the various steams or can be automatedusing processors and value actuation means. The hydrotreated effluentstream (9) exits the hydrotreater (4) at about 340-400° C., is cooled byheat exchange with the H₂S depleted stream (5) through recuperator (11),is sent through line (18) to cooler (19) and to absorber (8) of theamine treater to remove H₂S. The hydrocarbon product stream (20) willhave a low level of sulfur remaining, preferably below 20 ppm of sulfurcompounds. Absorber (8) is typically already present in the existingamine treater. Further processing can be done to this stream if desiredto remove sulfur with a solid sulfur adsorbent such as zinc oxide, ironoxide, activated carbon or caustic treatment or any other polishingsulfur removal technique to further reduce sulfur levels usingconventional systems.

Again referring to FIG. 1, an alternative operation is shown forsituations in which the ROG feed stream contains a high concentration ofolefins and is provided to the sulfur removing process at either high orlow pressures. For the purpose of this invention, high pressures are 10bar or greater and low pressures are less than 10 bar. In thisembodiment, the hydrotreater (4) can be bypassed by closing valves (13)and (68) and opening valve (10). In this manner, the olefin containingROG feed stream (3) can be processed without the conventionalhydrotreater (4) with the effluent stream (7) exiting the catalyticreactor (2) and bypassing hydrotreater (4) through bypass value (10) asshown. This embodiment is shown in a bypass mode with bypass valvespresent for ease of explanation, but can be employed as a stand alonesulfur removal system wherein hydrotreater (4) and bypass values (13,68, and 10) are excluded from the process.

The ROG feed stream (3) containing a high olefin concentration as wellas a high H₂S content is provided to absorber (12) at a low pressure,such as less than 10 bar, and treated by absorber (12) to reduce the H₂Scontent, preferably to less than 20 ppm. The H₂S depleted stream (5) ,leaves adsorber (12) with a high olefin content, and passes intocatalytic reactor (2) through line (15) which is not split (valve 13being closed) and where it is mixed with oxygen sent from line (16).Optionally H₂S depleted stream (5) can be preheated by heater (14) asdescribed above. The oxygen from line (16) will react with the hydrogenpresent to produce water and heat thereby raising the temperature of theeffluent stream (7) exiting catalytic reactor (2) to between 250° C. and450° C., preferably between 300° C. and 400° C. Alternatively, when thepressure of the RGP stream (3) is high, 10 bar or higher and preferablyabove 15 bar, the catalytic reactor (2) can operate solely inhydrogenation mode with no oxygen addition (the oxygen flow beingstopped in such situation). The required heat will be provided in thissituation by the hydrogenation of olefins contained in stream (15). Themajority of the organic sulfur compounds in the ROG feed stream (3),more than 60% and preferably 70%, will convert to H₂S from either theoxidation and/or hydrogenation reactions provided that the temperatureof the effluent stream (7) remains above 300° C. The effluent stream (7)bypasses the hydrotreater (4) through bypass valve (10), is cooled bypreheating with H₂S depleted stream (5) exiting adsorber (12) throughrecuperator (11) and sent through line (18) to cooler (19) to bring thegas stream to near ambient temperature before being sent to absorber (8)of the amine treater. Again, the amine treater (8) removes H₂S to lowlevels, such as below 20 ppm of sulfur compounds.

In another embodiment of this invention, two ROG streams are processedfor the removal of sulfur. These ROG feed streams are either alreadyreceived separately in the refinery or can be segregated into two ROGfeed streams. One of the streams will contain high concentrations ofolefins (5% or greater by volume) and one stream will contain lowconcentrations of olefins (3% or less by volume).

Referring now to FIG. 2, a first ROG feed stream containing a higholefin concentration (40) is sent through amine absorber (50), exits asa first H₂S depleted stream (21) and is split into a first split stream(24) and a second split stream (22). A second ROG feed stream containinga low olefin concentration (42) is sent through amine absorber (52) andexits as a second H₂S depleted stream (28). Second H₂S depleted stream(28) joins first split stream (24) to form first combined stream (31)which is sent through recuperator (27) and to the hydrotreater (40).Hydrotreater (40) converts the organic sulfur compounds within the firstcombined stream (31) to H₂S and hydrogenates the olefins containedwithin first combined stream (31) to provide the heat required for theconversion reaction. The second split stream (22) is optionally mixedwith oxygen fed through line (25) and sent to the catalytic reactor (30)to convert organic sulfur compounds to H₂S. If the pressure and sulfurconcentration of second split stream (22) is such that the olefinshydrogenate to raise the reactor temperature to above about 340° C., nooxygen is added and the oxygen flow is stopped. If the hydrogenationreactions are not sufficient to raise the temperature above about 340°C., then oxygen is added which will react with the hydrogen present toproduce additional heat to raise the temperature to about 340-400° C.Generally, above 10 bar or greater and preferably above 15 bar,catalytic reactor (30) can operate in the hydrogenation mode with nooxygen addition and no oxygen is introduced into second split stream(22). In this case, the required heat to sustain the reaction isprovided by the hydrogenation of olefins.

The organic sulfur depleted gas exiting catalytic reactor (30) andhydrotreater (40) exiting through lines (26) and (29), respectively, arecombined to form a second combined stream (32) and cooled by preheatingwith a second H₂S depleted ROG feed stream (31) through recuperator(27). The cooled product stream (33) is sent to the amine treater (54)for H₂S removal to provide a hydrocarbon stream with low sulfurconcentration, such as below 20 ppm. By varying the mixing volumes andflow ratio of the first split stream (24) having a high olefinconcentration and the second H₂S depleted ROG feed stream (28) having alow olefin concentration, the appropriate concentration of olefins inthe first combined stream (31) can be sent to hydrotreater (40) tomaintain the temperature at the desired window of operation, from about340° C.-450° C. Determining the mixing volumes is easily done by oneskilled in the art after measuring the olefin concentration of the ROGfeed streams and considering the process and temperature requirements.

Other variations of the present invention include the use of alternativesulfur removal systems in place of the amine treater. Although theinvention has been described in detail with reference to certainembodiments, those skilled in the art will recognize that there areother embodiments of the invention within the spirit and the scope ofthe claims.

1-24. (canceled)
 25. A process for the removal of H₂S and organic sulfurcompounds from a refinery off gas feed stream containing at leasthydrogen and a low concentration of olefins wherein the hydrogen toolefin molar ratio is greater than 0.5, comprising: a) removing at leasta portion of the H₂S from the feed stream by passing the feed streamthrough an amine absorber to produce a H₂S depleted stream; b) feedingthe H₂S depleted stream into a catalytic reactor at a temperaturebetween 340° C. and 450° C. to convert a majority of the organic sulfurcompounds to H₂S at the pressure employed; c) cooling the product gasstream exiting the catalytic reactor; and d) feeding the cooled productgas stream to an amine sulfur removal system to remove the H₂S andproduce a product gas stream.
 26. The process of claim 25 wherein thecatalytic reactor is a dual mode reactor capable of operating in ahydrogenation mode or an oxidation mode at space velocities of greaterthan 10,000 hr⁻¹.
 27. The process of claim 25 wherein the catalyticreactor employs a catalyst that contains a group VIII metal.
 28. Theprocess of claim 25 wherein the H₂S depleted stream is sent into thecatalytic reactor with the addition of oxygen.
 29. The process of claim25 wherein the H₂S depleted stream has a pressure of 10 bar or greaterand the catalytic reactor operates without the addition of oxygen.